1. Field of the Invention
This invention relates to solar water heater systems and more particularly to an apparatus for controlling water flow and isolating water in a solar heater system.
2. Information Disclosure Statement
Solar energy has been widely used to heat water for such things as residential use and swimming pools. Most such systems employ a solar collector which receives the radiant solar energy and directs it into the water to be heated. Circulation of water through the solar collector is desirable in such systems so that the heat acquired by the water in the solar collector may be transferred to a reservoir such as a hot water tank for future use. Circulation of the water by convection is generally unsatisfactory, and therefore forced circulation by use of a pump has been generally employed in such systems. Certain control means are typically employed to avoid losing energy from the system, as well as to avoid absorbing too much energy into the system. Such control means normally include temperature sensors and control circuits which permit the pump to circulate water in the system only when the sensed temperature of the water in the solar collector is higher than the sensed temperature of water in the reservoir or water tank. High temperature sensing means are also employed to stop the circulation of the water and thereby avoid overheating the water in the tank when too much radiant solar energy is absorbed by the system. Such systems are usually connected to a residential hot water supply system, and it is therefore also desirable to employ valve means to directly control the flow of water in the solar heater system, in addition to control of the circulation pump. The use of valve means in such a system also provides for automatic drainage of the system in the event of a power outage or a sensed low temperature condition which could freeze the water in the solar collector and thereby damage the solar collector. Even without experiencing freezing temperatures, however, a problem known as nighttime thermosiphoning or backsiphoning is experienced in such systems unless special precautions are taken. In those latitudes in which solar heating of water is economically feasible, there is always a period of darkness in each 24 hour period. During those periods of darkness, thermal energy from the water in the solar collector tends to be radiated into the atmosphere, and the water temperature in the hot water tank is typically significantly above that in the solar collector. Thus convection currents may be set up, and the phenomenon known as thermosiphoning occurs, in which the hot water from the hot water tank is conducted through the interconnecting plumbing to the solar collector where the hot water radiates thermal energy into the atmosphere before returning as cooler water to the hot water tank. Without the input of auxiliary heat from a gas or electric immersion heater, experience has shown that the water in a typical 40-gallon hot water tank may drop 14.degree. F. or more during the night in an open system. Of course, typical systems employ auxiliary heat, with the result that thermosiphoning merely serves to pump thermal energy from the auxiliary heater ultimately into the atmosphere where it is lost to the hot water system. Perhaps the most common way of reducing nighttime circulation due to thermosiphoning is to employ one or more spring-loaded check valves within the system. Although the use of check valves is one of the most common methods heretofore used to prevent thermosiphoning, it has two serious drawbacks. First, such check valves tend to restrict the flow of water unduly in the normal operating mode. Secondly, such spring-loaded check valves tend to become clogged with scale and either become stuck in the open position or fail to close completely so that at least some degree of thermosiphoning still occurs. The use of a "heat trap" alone produces results inferior to those of check valves. Separate motor driven valves may be employed in such systems with results superior to that of the spring-loaded check valve, but system complexity and cost is increased considerably, and reliability suffers. The prior art has failed to provide an apparatus for preventing nighttime thermosiphoning in a solar water heating system which is reliable, effective and inexpensive.
Therefore, it is an object of this invention to provide an apparatus which overcomes the aforementioned inadequacies of the prior art devices and provides an improvement which is a significant contribution to the advancement of the pertinent art.
Another object of this invention is to provide a solar heater control system for use with a water reservoir and a solar collector comprising a single valve means for controlling water flow in the solar heater system, a pump for circulating water in the solar heater system, means for sensing the temperature of the water in the reservoir and in the solar collector, and control means for controlling the operation of the pump and the valve means as a function of the temperatures sensed in the reservoir and the solar collector.
Another object of this invention is to provide a solar heater control system including a single valve means for permitting fluid communication between the circulating pump and the solar collector so that water may circulate from the reservoir to the collector, and simultaneously permitting fluid communication between the outlet of the collector and the water reservoir for conducting the solar heated water into the reservoir.
Another object of this invention is to provide a solar heater control system including a single valve means which provides for automatically draining the water from the solar collector when excessively high or excessively low temperatures are sensed in the water in the solar collector.
Another object of this invention is to provide a solar heater control system including a single valve means which prevents nighttime thermo-siphoning by stopping fluid communication between the solar collector and the reservoir and pump when the requisite heating conditions are not met and simultaneously when the conditions prerequisite for draining of the solar collector are not present.
Other objects and a fuller understanding of this invention may be had by referring to the summary of the invention, the description and the claims, taken in conjunction with the accompanying drawings.